Surfactant-associated electrochemical properties of ferrocene adsorbed on a glassy carbon electrode modified with multi-walled carbon nanotubes

The electrochemical properties of ferrocene (Fc) on a glassy carbon (GC) electrode modified by multi-walled carbon nanotubes (MWNTs) in the presence and absence of surfactants have been investigated by progressively voltammetric sweeping. Dihexadecyl phosphate (DHP) and hexadecyl trismethyl ammonium chloride (HTAC) are found to impact the redox reactions of Fc adsorbed on MWNT surfaces. An excess amount of DHP dispatches Fc from MWNTs surfaces, leading to weakly adsorbed configuration of Fc. The formal potential of the adsorbed Fc in the presence of DHP shifts to a lower potential. Cationic surfactant HTAC on MWNT surfaces depresses the redox reactions corresponding to the weakly adsorbed configuration of Fc. It becomes evident that the configuration and hence redox reactions of Fc depend strongly on the presence and concentrations of surfactants on the electrode surfaces and in the buffer solutions.     

Preparation and characterization of poly(indole-3-carboxaldehyde) film at the glassy carbon surface

Indole-3-carboxaldehyde (In3C) monomer was oxidized by electrochemical methods at the glassy carbon (GC) electrode in 0.05 M tetrabutylammonium tetrafluoroborate in acetonitrile, with the aim to prepare a modified electrode. Modification was performed using cyclic voltammetry (CV) scanning from 0.0 V to 2.0 V at a scan rate of 50 mV s^− 1 for 10 cycles in 1 mM In3C monomer solution. The modified GC surface (In3C-GC) was characterized by CV response of potassium ferricyanide and ferrocene redox probes as well as by the electrochemical impedance spectroscopy. The modified surface was analyzed by reflection-absorption infrared spectroscopy and compared with the spectrum of the monomeric In3C. Elemental composition of the surface was determined by X-ray photoelectron spectroscopy. Contact angle measurements was also performed to check the changes in hydrophobic character of the bare GC and compared to that of In3C-GC surface. Thickness of the oligomeric/polymeric film was investigated by ellipsometric measurements and a surface confined polymerization mechanism was proposed.     

Electrochemical degradation of benzene in natural water using silver nanoparticle-decorated carbon nanotubes

In this study, a novel methodology for the electrochemical degradation of benzene in natural water using silver nanoparticle-decorated carbon nanotubes has been investigated. The morphology, the structure, and the electrochemical performance of the multi-walled carbon nanotubes-silver (MWCNT-Ag) nanocomposite film were characterised by transmission electron microscopy (TEM), X-ray diffraction (XRD), and cyclic voltammetry (CV), respectively. Electrocatalytic oxidation of benzene in an aqueous solution was studied to evaluate potential applications of the MWCNT-Ag modified glassy carbon (GC) electrode in environmental science. The benzene removal efficiency in natural water containing 10 mg L⁻¹ benzene yielded 77.9% at an applied potential of +2.0 V for 2 h using the MWCNT-Ag-GC electrode. In comparison, the removal efficiency reached only 8.0% with the bare GC electrode, showing the suitability of the MWCNT-Ag nanocomposite modified GC electrode for electro-oxidation of benzene in natural water.     

Facile preparation and characterization of free-standing stiff carbon-based composite films with excellent performance

Novel free-standing stiff all carbon films based on multi-walled carbon nanotube (MWNT)/glassy carbon (GC) with excellent performance were fabricated. MWNTs, as excellent reinforcing materials, were successfully dispersed in polyimide (PI) matrix by in situ polymerization. The resultant MWNT/PI nanocomoposite films were used as precursors and underwent carbonization process. As a result, all carbon constituted MWNT/GC composite films were obtained. Mechanical results showed the maximum 3-point bending strength and modulus reached 575.5 MPa and 7.7 GPa respectively, improved by 54% and 78% compared to those of neat GC films. This method is simple, and the free-standing composite films can be prepared in large scales, which hold great potential in many applications.     

Modified carbon surfaces as "organic electrodes" that exhibit conductance switching

Glassy carbon (GC) surfaces modified with monolayers of biphenyl and nitrobiphenyl molecules were examined as voltammetric electrodes for ferrocene, benzoquinone, and tetracyanoquinodimethane electrochemistry in acetonitrile. The modified electrodes exhibited slower electron transfer than unmodified GC, by factors that varied with the monolayer and redox system. However, after a negative potential excursion to approximately -2.0 V versus Ag+/Ag, the modified electrodes exhibited much faster electron-transfer kinetics, approaching those observed on unmodified GC. The effect is attributed to an apparently irreversible structural change in the biphenyl or nitrobiphenyl monolayer, which increases the rate of electron tunneling. The transition to the "ON" state is associated with electron injection into the monolayer similar to that observed in previous spectroscopic investigations and causes a significant decrease in the calculated HOMO-LUMO gap for the monolayer molecule. Once the monolayer is switched ON, it supports rapid electron exchange with outer-sphere redox systems, but not with dopamine, which requires adsorption to the GC surface. The increase in electron-transfer rate with electron injection is consistent with an increase in electron tunneling rate through the monolayer, caused by a significant decrease in tunneling barrier height. The ON electrode can reduce biphenyl- or nitrobiphenyldiazonium reagent in solution to permit formation of a second modification layer of biphenyl or nitrobiphenyl molecules. This "double derivatization" procedure was used to prepare tetraphenyl- and nitrotetraphenyl-modified electrodes, which exhibit significantly slower electron transfer than their biphenyl and nitrobiphenyl counterparts. A "switching" electrode may have useful properties for electroanalytical applications and possibly in electrocatalysis. In addition, the ON state represents an "organic electrode" in which electron transfer occurs at an interface between an organic conductor and a solution rather than an interface between a solution and a metal or carbon electrode.     

全钒液流电池用碳纳米管-石墨复合电极的研究

将石墨(GP)和多壁碳纳米管(MWNT)按不同比例压片制成电极,用于全钒氧化还原液流电池电极材料,通过循环伏安、交流阻抗、充放电测试、SEM手段对MWNT-GP复合电极进行表征和分析.研究结果表明,MWNT含量为15wt%的MWNT-GP复合电极性能最佳,对组装成的静态电池在电流密度20~80mA/cm2进行充放电性能比较,电流效率均在93%以上,电压效率随着电流密度的增加而有所下降.     

Direct electron transfer and biosensing of glucose oxidase immobilized at multiwalled carbon nanotube-alumina-coated silica modified electrode

Investigations are reported regarding the direct electrochemical performance of glucose oxidase (GOD) immobilized on a film of multiwalled carbon nanotube-alumina-coated silica (MWCNT-ACS). The surface morphology of the GOD/MWCNT-ACS nanobiocomposite is characterized by scanning electron microscopy. In cyclic voltammetric response, the immobilized GOD displays a pair of well-defined redox peaks, with a formal potential (E°′) of ? 0.466 V versus Ag/AgCl in a 0.1 M phosphate buffer solution (pH 7.5) at a scan rate of 0.05 V s^? 1; also the electrochemical response indicates a surface-controlled electrode process. The dependence of formal potential on solution pH indicates that the direct electron transfer reaction of GOD is a reversible two-electron coupled with a two-proton electrochemical reaction process. The glucose biosensor based on the GOD/MWCNT-ACS nanobiocomposite shows a sensitivity of 0.127 A M^? 1 cm^? 2 and an apparent Michaelis–Menten constant of 0.5 mM. Furthermore, the prepared biosensor exhibits excellent anti-interference ability to the commonly co-existed uric acid and ascorbic acid.     

Electrochemical properties of carbon nanotube (CNT) film electrodes prepared by controllable adsorption of CNTs onto an alkanethiol monolayer self-assembled on gold electrodes

This paper describes electrochemical properties, such as electrode reactivity, electrode dimensions, and interfacial capacitance, of multiwalled carbon nanotube (MWNT) film electrodes prepared by controllable adsorption of the MWNTs onto the self-assembled monolayer (SAM) of n-octadecyl mercaptan (C18H37SH) deposited onto Au electrodes. The adsorption of the MWNTs onto the SAM-modified Au electrode substantially restores heterogeneous electron transfer between bare Au electrode and redox species in solution phase that is almost totally blocked by the SAM of C18H37SH, and as a result, the prepared MWNT/SAM-modified electrode possesses good electrode reactivity without a remarkable barrier to heterogeneous electron transfer. In addition, the surface coverage of the MWNTs is readily controlled by adjusting the immersion time for the adsorption of the MWNTs onto the SAM of C18H37SH, which essentially endows the prepared MWNT/SAM-modified electrodes with tunable electrode dimensions ranging from a nanoelectrode array to a macro-sized conventional electrode. On the other hand, the MWNT/SAM-modified electrode is found to possess a largely reduced interfacial capacitance, as compared with the MWNT film electrodes prepared with existing methods by directly confining the MWNTs onto electrode surface. This demonstration offers a new approach to fabrication of stable MWNT film electrodes with excellent electrochemical properties that are believed to be very attractive for electrochemical studies and electroanalytical applications.     

Synthesis of nickel oxides nanoparticles on glassy carbon as an electron transfer facilitator for horseradish peroxidase: Direct electron transfer and H2O2 determination

In this study, horseradish peroxidase/nickel oxides nanoparticles/glassy carbon (HRP/NiO NPs/GC) electrode was prepared by first applying nickel oxides nanoparticles on glassy carbon surface and then horseradish peroxidase immobilized on the NiO NPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used as a diagnostic tools to identify the synthesized NiO NPs. Immobilized HRP showed an electrochemical redox behavior pertained to HRP(Fe(III)–Fe(II)) by direct electron transfer between protein and nanoparticles with a formal potential (E^0′) of ? 55.5 mV (vs. Ag/AgCl and 141.5 mV vs. NHE) in 50 mM phosphate buffer solution (PBS). The anodic charge transfer coefficient (α) and heterogeneous electron transfer rate constant (k_s) were 0.42 and 0.75 s^? 1, respectively. Biocatalytic activity of HRP/NiO NPs/GC electrode for reduction of hydrogen peroxide and application to hydrogen peroxide determination was exemplified.     

Electrochemical horseradish peroxidase biosensor based on dextran–ionic liquid–V2O5 nanobelt composite material modified carbon ionic liquid electrode

Direct electrochemistry of horseradish peroxidase (HRP) was realized in a dextran (De), 1-ethyl-3-methylimidazolium ethylsulphate ([EMIM]EtOSO₃) and V₂O₅ nanobelt composite material modified carbon ionic liquid electrode (CILE). Spectroscopic results indicated that HRP retained its native structure in the composite. A pair of well-defined redox peaks of HRP appeared in pH 3.0 phosphate buffer solution with the formal potential of ?0.213 V (vs. SCE), which was the characteristic of HRP heme Fe(III)/Fe(II) redox couple. The result was attributed to the specific characteristics of De–IL–V₂O₅ nanocomposite and CILE, which promoted the direct electron transfer rate of HRP with electrode. The electrochemical parameters of HRP on the composite modified electrode were calculated and the electrocatalysis of HRP to the reduction of trichloroacetic acid (TCA) was examined. Under the optimal conditions the reduction peak current increased with TCA concentration in the range from 0.4 to 16.0 mmol L^?1. The proposed electrode is valuable for the third-generation electrochemical biosensor.     

Carbon nanotube/graphene nanocomposite as efficient counter electrodes in dye-sensitized solar cells

We demonstrated the replacement of the Pt catalyst normally used in the counter electrode of a dye-sensitized solar cell (DSSC) by a nanocomposite of dry spun carbon multi-walled nanotube (MWNT) sheets with graphene flakes (Gr-F). The effectiveness of this counter electrode on the reduction of the triiodide in the iodide/triiodide redox (I(-)/I(3)(-)) redox reaction was studied in parallel with the use of the dry spun carbon MWNT sheets alone and graphene flakes used independent of each other. This nanocomposite deposited onto fluorinated tin-oxide-coated glass showed improved catalytic behavior and power conversion efficiency (7.55%) beyond the use of the MWNTs alone (6.62%) or graphene alone (4.65%) for the triiodide reduction reaction in DSSC. We also compare the use of the carbon MWNT/Gr-F composite counter electrode with a DSSC using the standard Pt counter electrode (8.8%). The details of increased performance of graphene/MWNT composite electrodes as studied are discussed in terms of increased catalytic activity permitted by sharp atomic edges that arise from the structure of graphene flakes or the defect sites in the carbon MWNT and increased electrical conductivity between the carbon MWNT bundles by the graphene flakes.     

Fabrication and electrochemical behavior of single-walled carbon nanotube/graphite-based electrode

An electrochemical method for determining the dihydroxybenzene derivatives on glassy carbon (GC) has been developed. In this method, the performance of a single-walled carbon nanotube (SWCNT)/graphite-based electrode, prepared by mixing SWCNTs and graphite powder, was described. The resulting electrode shows an excellent behavior for redox of 3,4-dihydroxybenzoic acid (DBA). SWCNT/graphite-based electrode presents a significant decrease in the overvoltage for DBA oxidation as well as a dramatic improvement in the reversibility of DBA redox behavior in comparison with graphite-based and glassy carbon (GC) electrodes. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) procedures performed for used SWCNTs.     

Fabrication and electrocatalysis of self-assembly directed gold nanoparticles anchored carbon nanotubes modified electrode

A self-assembly directed approach was adopted to modify glassy carbon electrode (GC) with gold nanoparticles incorporation and the electrocatalytic performance of self-assembly modified electrode, GC/SA-Au-ME was critically evaluated for the oxidation of ascorbic acid (AA). The modification involves the dispersion of multi-wall carbon nanotube (MWNT) and an inclusion complex, beta-cyclodextrin-4-aminothiophenol on the surface of GC electrode in the presence of cetyltrimethylammonium bromide (CTAB). Gold nanoparticles were deposited into the self-assembled sites to fabricate the modified electrode, GC/SA-Au-ME. Another electrode (GC-Au-ME) was fabricated under similar conditions in the absence of CTAB. The electrocatalytic activity of the modified electrodes (GC/SA-Au-ME and GC-Au-ME) towards the oxidation of AA was critically compared. Cyclic voltammetry, chronoamperometry, and double potential chronoamperometry were used to evaluate the characteristics of the modified electrodes. The self-assembled electrode (GC/SA-Au-ME) shows excellent electrocatalytic activity over the other electrode, GC-Au-ME. Augmented current response, faster electron transfer kinetics (with a rate constant for electron transfer process as 3.25 x 10(4) cm3 mol(-1) s(-1)), linear range of response for the analyte (1-50 mM with an extended detection limit to 1 microM), better sensitivity, and selectivity were witnessed for the self-assembly directed modified electrode.     

Preparation and electrochemical properties of nitrogen-doped multi-walled carbon nanotubes

High yield bamboo-shaped N-doped multi-walled carbon nanotubes (MWNTs), containing 2.27 at.% N, were fabricated by pyrolysis of pyridine at 800 °C in an Ar atmosphere. The electrochemical capacitive performances of this type of carbon fiber were evaluated in 6 M KOH aqueous solution. The specific capacitance of N-doped MWNT electrode is measured to be 44.3 F/g at the charge/discharge current of 1 mA, which is two times greater than that of the undoped one (19.9 F/g). The measurements also reveal that the N-doped MWNT electrode possesses lower equivalent series resistance (0.24 Ω) and higher knee frequency (1995 Hz) than the undoped one. This improvement is attributed to the unique morphology and electronic properties of N-doped MWNTs.     

Multiwall carbon nanotube and poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) composite films for transistor and inverter devices

Highly conductive multiwalled carbon nanotube (MWNT)/Poly(3,4-ethylenedioxythiophene) polymerized with poly(4-styrenesulfonate) (PEDOT:PSS) films were prepared by spin coating a mixture solution. The solution was prepared by dispersing MWNT in the PEDOT:PSS solution in water using ultrasonication without any oxidation process. The effect of the MWNT loading in the solution on the film properties such as surface roughness, work function, surface energy, optical transparency, and conductivity was studied. The conductivity of MWNT/PEDOT:PSS composite film was increased with higher MWNT loading and the high conductivity of MWNT/PEDOT:PSS films enabled them to be used as a source/drain electrode in organic thin film transistor (OTFT). The pentacene TFT with MWNT/PEDOT:PSS S/D electrode showed much higher performance with mobility about 0.2 cm2/(V s) and on/off ratio about 5 × 10? compared to that with PEDOT:PSS S/D electrode (～0.05 cm2/(V s), 1 × 10?). The complementary inverters exhibited excellent characteristics, including high gain value of about 30.     

Fabrication of amperometric xanthine biosensors based on direct chemistry of xanthine oxidase

The construction of amperometric xanthine biosensor by immobilization of xanthine oxidase (XOD) on the multi-wall carbon nanotubes (CNTs) modified glassy carbon (GC) electrode surface was investigated. The direct chemistry of XOD was accomplished and the formal potential was about − 0.465 V (vs SCE). The heterogeneous electron transfer rate constant was evaluated to be 2.0 ± 0.3 s^− 1. The xanthine biosensor based on XOD entrapped in silica sol–gel (SG) thin film on CNTs-modified GC electrode surface was also investigated. The XOD still maintains its activity to xanthine. The amperometric response to xanthine showed a linear relation in the range from 0.2 µM to 10 µM and a detection limit of 0.1 µM (S/N = 3). The enzyme electrode retained 95% of its initial activity after 90 days of storage. The sensor exhibited high sensitivity, rapid response and good long-term stability.     

Fabrication of graphene–platinum nanocomposite for the direct electrochemistry and electrocatalysis of myoglobin

In this paper a platinum (Pt) nanoparticle decorated graphene (GR) nanosheet was synthesized and used for the investigation on direct electrochemistry of myoglobin (Mb). By integrating GR–Pt nanocomposite with Mb on the surface of carbon ionic liquid electrode (CILE), a new electrochemical biosensor was fabricated. UV-Vis absorption and FT-IR spectra indicated that Mb remained its native structure in the nanocomposite film. Electrochemical behaviors of Nafion/Mb–GR–Pt/CILE were investigated with a pair of well-defined redox peak appeared, which indicated that direct electron transfer of Mb was realized on the underlying electrode with the usage of the GR–Pt nanocomposite. The fabricated electrode showed good electrocatalytic activity to the reduction of trichloroacetic acid in the linear range from 0.9 to 9.0 mmol/L with the detection limit as 0.32 mmol/L (3σ), which showed potential application for fabricating novel electrochemical biosensors and bioelectronic devices.     

Electrochemistry of Cu(I) doped CdS nanoparticles hosted by DNA–CTMA in aqueous electrolyte

The electrochemical redox behaviors of Cu(I) doped CdS nanoparticles in DNA–CTMA films are investigated in aqueous electrolyte. Both oxidation and reduction processes are electrochemically irreversible. The degradation of nanoparticles and the coupled chemical reactions in the electrochemical measurements can be avoided by fast potential scan as 1.5 V s⁻¹. It is hardly found the residual O₂ effect on the redox behavior of nanoparticles in DNA–CTMA film. The role of DNA–CTMA matrix in the charge transfer process between nanoparticles and the electrode is discussed.     

Direct electrochemical behavior of cytochrome c on sodium dodecyl sulfate modified electrode and its application to nitric oxide biosensor

Polyacrylamide (PAM), sodium dodecyl sulfate (SDS) and cytochrome c (Cyt c) were immobilized on the surface of a glass carbon electrode (GCE), respectively, to form a Cyt c /SDS/PAM/GCE. The modified electrode was characterized with the electrochemical impedance. The direct electrochemical behaviors of Cyt c on SDS/PAM/GCE were obtained by using cyclic voltammetry. A pair of well-defined and reversible redox peaks could be observed in a 0.10 M pH 7.0 phosphate buffer solution. The anodic and cathodic peak potentials of Cyt c were at 0.051 V and − 0.003 V (vs. Ag/AgCl), respectively. The Cyt c on SDS/PAM/GCE exhibited well electrocatalytic activity to reduction of nitric oxide. The relative electrochemical parameters were obtained. The resulted electrode displayed a rapid amperometric response to the reduction of nitric oxide. The catalytic current is linear to the nitric oxide concentration in the range of 8.0 × 10^− 7 M to 9.5 × 10^− 5 M and the detection limit was 1.0 × 10^− 7 M (Signal/Noise = 3). The proposed biosensor could be used to detect quantitatively nitric oxide.     

Voltammetric determination of ethamsylate in bulk solution and pharmaceutical tablet by nano-material composite-film coated electrode

A sensitive electrochemical method was described for voltammetric determination of ethamsylate at a glassy carbon electrode (GCE) coated with a nano-material thin film. In this work, a nanometer material, namely, multi-wall carbon nanotubes (MWCNT) was dispersed successfully into water in the presence of dihexadecyl hydrogen phosphate (DHP) and a MWCNT–DHP composite film was conveniently obtained on the GCE surface. The electrochemical behavior of ethamsylate at this modified electrode was investigated and a pair of reversible redox peak was observed. Compared with the electrochemical response of ethamsylate at the bare GCE, the separation of peak potential (ΔE_p) of ethamsylate decreased obviously from 438 to 40 mV and the current density of redox peaks increased greatly. Based on this, differential pulse voltammetry (DPV) was employed to determine ethamsylate. Various experimental parameters such as pH value of the supporting electrolyte, the amount of modifier and so on were optimized. Under optimal conditions, a linear response of ethamsylate was obtained in the range from 1.0 × 10^− 6 to 2.0 × 10^− 5 mol/L, and the detection limit was 6.0 × 10^− 7 mol/L. The proposed method was successfully applied to detect ethamsylate in pharmaceutical samples.